Applicants have recently molded lensed ferrules comprise an array of lenses and one or more mechanical alignment elements. The lenses are typically in a linear array with a pitch of 0.25 mm and a diameter slightly less than 0.25 mm, for example, 0.24 mm. The alignment elements are typically pins and/or holes with a diameter of 0.7 mm. In one embodiment, the ferrules are hermaphroditic, meaning that a given ferrule has an alignment pin and an alignment hole such that identical ferrules can mate with one another.
It is critical to the performance of the lensed ferrule that the lenses be precisely located with respect to the mechanical alignment elements. For example, when two lensed ferrules are mated to each other, the mechanical alignment elements guide the two parts such that the corresponding lenses will be aligned. Any deviation from this alignment will result in increased loss, and possible loss of function of the optical device. Therefore a molded part should be formed that has a precise relationship between the locations of the mechanical alignment elements and the optical components (lenses, fibers, etc.).
When creating such molded components, the mold is typically built from several pieces of mold “steel,” which can be adjusted slightly as the mold is “conditioned” or tuned. The mold is typically inspected for accuracy. However, the molded part must meet optical and therefore dimensional tolerances. The final conditioning of the mold is therefore made by inspecting molded pieces and adjusting the mold accordingly. Acceptance of the mold is based on a “first article” inspection of the molded pieces, which consists of a measurement of all dimensions on the product based on several representative pieces. For these reasons, it is necessary to be able to accurately measure the locations of the optical and mechanical elements of a molded component.
Accurate measurements of a molded part can be made visually, using a camera, lens system, and precision translation stages. However, because the dimensions and geometries of the lenses and mechanical alignment elements are significantly different, Applicant recognizes that a measurement of the relative locations of the lenses and mechanical alignment elements can be difficult. For example, systematic errors may be introduced by lighting, which may affect one geometry, such as a lens, in a different manner than it affects another geometry, such as a hole.
Furthermore, Applicant recognizes that the edges of a molded part are often not perfectly sharp. For example, the material being molded may not fill the corners of the mold. Also, it may not be possible to machine sharp corners for some elements of the mold, thereby resulting in rounded edges in the molded plastic part. In this respect, some edges are even configured to be rounded—e.g., alignment pins are typically configured with a chamfered edge to function as a lead in when the alignment pin is inserted into an alignment hole during mating. Because rounded edges are not clearly defined, they complicate accurate visual measuring of the molded part.
For example, referring to FIGS. 1-2, a hermaphroditic ferrule 100 is shown which uses pin/hole alignment elements 104, 105 to align mating ferrules. The ferrule 100 comprises a linear array of lenses 103. Such a part is particularly difficult to inspect visually as shown in FIG. 2. The pin 104, hole 105, and lenses 103 all have a different characteristic appearance, which depends significantly on the lighting conditions. The edge of the alignment pin 104 is particularly hard to determine, since it has a fillet 104a to facilitate mating with a like connector.
Therefore, a need exists for an approach of measuring the alignment among disparate elements on the surface of a molded optical component. The present invention fulfills this need among others.